Browser slows to crawl, then freezes

Im sure this is a common problem, but I have run adware, spybot, avast and even defragged and deleted my caches, but my windows 98 browser stopped working well shortly after downloading a virtual reality program. I dwloaded firefox and google chrome and soon after they began to slow down. I restored twice, it hasn't helped. I don't have any copies of windows operating systems. Basically it will slow down till I have to wait forever and then I log out in frustation. Usually after 30-60 min off, the longer the better, it works well before eventually slowing to a crawl again.

My computer comes with a free 3 month of norton but this time after restoring norton strangely stopped working, refused to dwload updates, rendering it useless and then I removed it and dwloaded Free Avast anti virus software.

Any hints on what I can do please? (pretty much a beginner here when it comes to computer repair) Thanks!!!!